Insights into the degradation mechanism of PET and PP under marine conditions using FTIR

Plastics possess diverse functional properties that have made them extremely desirable. However, due to poor waste management practices, large quantities eventually end up in the oceans where their degradation begins. Hence, it is imperative to understand and further investigate the dynamics of this process. Currently, most relevant studies have been carried out under benign and/or controlled weather conditions. This study investigates the natural degradation of polypropylene (PP) and polyethylene terephthalate (PET) in more extreme environments. Simulated and real marine conditions, both in the laboratory (indoors) and outdoors were applied for a duration of 140 days and results were assessed using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis. SEM micrographs revealed variations in the morphologies of both plastic types. Degradation signs were shown in both plastic types, under all conditions. Findings indicated that microplastics (MPs) degraded faster than macroplastics, with PP MPs having higher weight loss (49%) than PET MPs (1%) when exposed to outdoor marine conditions. Additionally, the degradation rates of MPs-PP were higher than MPs-PET for outdoor and indoor treatments, with 1.07 x 10-6 g/d and 4.41 x 10- 7 g/d, respectively. FTIR combined with PCA was efficient in determining the most degraded plastic types.

Automated summary

Plastics are highly desired due to their diverse functional properties, but their poor waste management leads to their eventual accumulation in the oceans and degradation. Therefore, understanding the dynamics of plastic degradation is crucial. This study investigates the natural degradation of polypropylene (PP) and polyethylene terephthalate (PET) in extreme marine conditions. Results show that microplastics (MPs) degrade faster than macroplastics, with PP MPs experiencing higher weight loss (49%) than PET MPs (1%) in outdoor marine conditions. This research provides valuable insights into the degradation rates of different plastic types.